When a Positron Emission Computed Tomography (PET) apparatus performs a scanning, each patient generally has to be scanned twice, with one scanning being the emission scanning and the other scanning being the transmission scanning. Data collected in the emission scanning substantially reflects distribution of a drug in the patients body. Since an attenuation correction is not performed on the data, the quantification is inaccurate. Data collected in the transmission scanning is specially used to generate an attenuation sinogram to perform the attenuation correction on the data obtained in the emission scanning. When the PET apparatus performs a cardiac examination, the data obtained in the emission scanning may reflect the distribution of the drug in the patient's body and the emission scanning takes approximately 4 minutes. Moreover, the transmission scanning takes approximately 30 minutes in order to obtain a relatively accurate scanning image.
According to the attenuation correction method in the prior art, Segmented Attenuation Correction (SAC) method is used to reduce the time spent on the transmission scanning and obtain a relatively accurate image. In this method, Filtered Back Projection (FBP) reconstruction is firstly performed on the data collected in the transmission scanning. The obtained FBP reconstruction image is divided into a tissue region, a lung region, a bed board region and an air region according to pixel values of the image. The four regions have four different densities respectively, and denote four different attenuation coefficients. Corresponding values are assigned to pixels of image the each of the regions. Then the forward projection is performed on the assigned image. A thus obtained attenuation sinogram is used in the attenuation correction performed on the data obtained by the emission scanning.
However, in the above attenuation correction method, the scan for one patient may have to last more than 10 minutes. Moreover, it may take even more than 1 hour to scan the whole body of a patient. Therefore, the efficiency of the attenuation correction for the medical image obtained by the PET apparatus scanning is still low. As a result, it is desired to propose an innovative attenuation correction method for a medical image, so as to ensure the precision of the image after the attenuation correction with the time spent by the transmission scanning being reduced, improve the input-output ratio of the apparatus and reduce psychological and physiological discomfort of the patient due to the scanning.